Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $236.59   3.277%   $244.3431   $244.34   $244.35   $244.30  
  Purchase #2 $45.48   9.295%   $49.7074   $49.71   $49.70   $49.70  
  Purchase #3 $225.86   3.291%   $233.2931   $233.29   $233.30   $233.30  
  Purchase #4 $224.85   3.279%   $232.2228   $232.22   $232.20   $232.20  
  Purchase #5 $127.84   3.513%   $132.331   $132.33   $132.35   $132.30  
  Purchase #6 $32.96   4.844%   $34.5566   $34.56   $34.55   $34.60  
  Purchase #7 $194.40   10.271%   $214.3668   $214.37   $214.35   $214.40  
  7 purchase totals = $1,087.98       $1,140.8208   $1,140.82   $1,140.80   $1,140.80